1. Field of the Invention
This invention relates generally to a hollow-fibre permeability apparatus, and more particularly to hollow-fibre permeability apparatus in which a permeating region of a housing contains a bundle of hollow fibres, and materials can selectively permeate through the membranes formed by the permeable walls of the hollow fibres, between a fluid flowing in the open spaces of the bundle of hollow fibres, and another fluid flowing inside the follow fibres. The permeation may be based on the principles of osmosis, dialysis, ultrafiltration, reverse osmosis or the like.
2. Description of the Prior Art
For example, a conventional hollow-fibre permeability apparatus is used for blood dialysis in an artificial kidney, in which toxic materials are removed from the blood of a patient suffering from renal failure or medicinal poisoning. Such apparatus is also used in an artificial lung, in which oxygen and carbon dioxide are exchanged with each other to increase the blood oxygen content.
An example of a conventional hollow-fibre permeability apparatus will now be described.
FIG. 1 shows a hollow-fibre blood dialysis apparatus 10 for use as an artificial kidney. The apparatus 10 comprises a cylindrical housing 1 formed of suitable material such as a synthetic resin. The housing 1 is open at both ends. Upper and lower cylindrical enlarged-diameter portions 37 and 38 are formed integrally with the housing 1. An inlet tube 2 and an outlet tube 3 for dialysate are connected to the enlarged portions 38 and 37, respectively, so as to be diametrically opposite to each other. Screw threads 8 are formed on the outer cylindrical surfaces of the end portion of the enlarged portion 37 and of the end portion of the enlarged portion 38.
A permeating region 25 in the housing 1 is filled with a hollow-fibre bundle 6 which consists of numerous hollow fibres 5 packed closely to each other. The hollow fibres 5 are made of suitable material, such as cellulose, and are substantially of the same length as the housing 1. Normally, the bundle 6 consists of ten to fifteen thousand hollow fibres 5, which are about 0.3 mm in diameter. The total membrane area of the hollow fibres 5 for effective dialysis is about 1 m.sup.2.
The end portions of the bundle 6 are potted in a potting material 7 such as polyurethane, silicone resin or epoxy resin. Upper and lower disc covers 13 contact the outer peripheral regions of the upper and lower surfaces of the potting material 7 in the upper and lower openings of the housing 1. Upper and lower fastening rings 17 and 18 are secured to the housing by the engagement of screw threads 21 with the screw threads 8, so that the potting material 7 and the disc covers 13 are held between the upper and lower ends of the housing 1 and inwardly directed flange portions 19 of the fastening rings 17 and 18. In this way the bundle 6 of hollow fibres 5 is fixed at both ends in the housing 1. The upper and lower ends of the hollow fibres 5 are cut so as to open flush with the upper and lower smooth surfaces of the potting material 7. The fastening rings 17 and 18 are formed of suitable material, such as a synthetic resin.
The upper and lower disc covers 13 also form blood inlet tube 14 and a blood outlet tube 15, respectively. The central regions 13A of the disc covers 13 are axially disposed to form circular compartments 20 adjuacent to and communicating with the inlet and outlet tubes 14 and 15, and also communicating with the interiors of the hollow fibres 5.
When blood is to be dialysed by the apparatus 10, dialysate 35 is supplied into the housing 1 from the inlet tube 2, and blood 36 to be dialysed, from an artery of a patient, is supplied into the housing 1 from the inlet tube 14. The dialysate 35 is distributed in an annular space 22 defined by the enlarged portion 38, and then passes into the bundle 6 of hollow fibres 5. The dialysate 35 passes upwardly through gaps or open spaces between the hollow fibres 5, into an annular space 23 defined by the enlarged portion 37, and out of the housing 1 through outlet tube 3. On the other hand, the blood 36 is distributed into the upper openings of the hollow fibres 5 from an inlet opening 24 of the tube 14 and the upper compartment 20. The blood 36 flows downwardly through the hollow fibres 5, counter-currently to the dialysate 35, and passes out of the housing 1 through the lower openings of the hollow fibres 5, the lower compartment 20 and the outlet tube 15.
The blood 36 is dialysed through the membrane walls of the hollow fibres 5 by the action of the dialysate 35. Accordingly, metabolic wastes such as urea, uric acid and creatinine can be removed from the blood 36 into the dialysate 35. The purified blood 36 passes out of the housing 1, and is returned to a vein of the patient. When the dialysate 35 is pumped out from the outlet tube 3, the dialysate 35 has negative pressure compared with the blood 36, so that ultrafiltration is effected between the dialysate 35 and the blood 36, to remove excess water from the blood 36.
The hollow fibres 5 used in the blood dialysis apparatus 10 provide a relatively large effective surface area of membrane. Therefore, the apparatus 10 can smaller than conventional coil-type or plate-type blood dialysis apparatus. Thus, the blood priming volume can be smaller, which is beneficial to the patient during dialysis. The apparatus 10 is also easier to handle, and the hollow fibres 5 are superior in withstanding pressure and for ultrafiltration.
Since the blood dialysis apparatus 10 has many advantages as above described, it has become popular recently. However, the apparatus 10 has the following disadvantages.
Since the ten to fifteen thousand hollow fibres 5 are closely bundled in the housing 1, it is difficult for the dialysate 35 to pass uniformly through the whole of the bundle 6. It is experimentally proved that the dialysate flow rate is higher around the peripheral region of the bundle 6 adjacent to the inner surface of the housing 1, and the dialysis is extremely low in the central region of the bundle 6. It is also found that boundary layers are formed along the outer and inner surface of the hollow fibres 5 which reduce the dialysis efficiency.